The Mortality Rune
by amabethchase
Summary: Clary invents a rune to make Simon mortal again. Will it work? And how long will he STAY human? (HEAVY ON THE SIZZY).
1. Chapter 1

**Chapter One**

"I have a birthday present for you."

Simon glanced up from the comic book he was reading in bed. He was sleeping in the guest bedroom at Luke's place, and he'd thought Clary would be at Jace's. He was glad she wasn't.

Simon sighed. "Clary, you don't have to get me anything-"

"No," she said, smiling. "But I don't think you'll object to this."

Simon opened his mouth to ask what she was holding behind her back, but Clary only pulled out her stele as she moved over to sit at the foot of his bed.

"I'm not sure this will work," she said slowly, cautiously, "But I hope it will."

"Clary," Simon said, biting back laughter, "I know I'm as cool as one, but I'm not a Shadowhunter. I guess I could frame the stele or something, but don't you kind of need it?"

Clary grinned. Her green eyes sparkled with anticipation. "I've been working on a rune for a while," she said, locking her gaze with his. "If it works correctly, it will . . . it will turn you back into a mortal."

Simon recoiled. "So, no more blood?"

"Only if you want it."

"You could make me human again?" Simon tried to not sound too hopeful, but the prospect was too exciting. Too many scenarios raced through his head; his mother might let him back home. He could visit Isabelle in the Institute. He wouldn't have to grow old with a warlock who didn't even know his name while all his friends, and Izzy, died.

"I hope so." Clary spoke quietly. She _was _hopeful, Simon realized. Too hopeful.

"Clary, I don't want you to feel like you've failed me if this doesn't work," Simon said.

"It will work," Clary said firmly, straightening her back, newly confident. "I'm going to make you human."

"All right." If Simon had a heartbeat, it would be racing. He set the comic book down and extended his arm. "Mark me up, Fray."

Clary smiled. Her hand shook slightly as she raised the stele to his pale, icy skin. She shut her eyes.

"Clary!" Simon shouted.

"What?" She shouted too, jumping back.

"You have to _look," _he said nervously.

"Trust me," she insisted, and he did.

She shut her eyes again, and set the stele on his right forearm. It was still odd looking at his arms and not seeing any vein, any imperfections, anything. Maybe he wouldn't have to for much longer.

Clary began to draw, dragging her stele slowly over his skin and searing it. He winced at the pain, but tried to remain still so the rune would have a maximum effectiveness.

It felt like hours as Clary drew the rune, though it was merely minutes; Simon was anxious and wanted desperately to know if it was working, if it was bad that he wasn't feeling any different, if she was done, but he did not want to distract her.

Finally the stele lifted from Simon's skin, and the burning sensation dulled.

Clary slid back, several feet away, looking even more anxious than Simon felt.

"Did it work?" Simon asked.

"You tell me," Clary said quietly. She was transfixed on the Mark she'd sketched on his arm. It did not look too different from the other runes Simon had seen the Shadowhunters wear; full of curves and dashed lines and resembling a Satanic symbol of some kind. But so far he felt no different.

He was just about to heave a sigh of defeat, assure Clary it was okay, he didn't doubt her abilities-in fact, he was confident in them-but he was not disappointed. When suddenly he _did _feel different.

His heart began beating.

It jolted like a car with a touchy gas pedal, and Simon jumped slightly, gripping his chest as he felt blood begin to pump out of his heart again, through his veins, through his arms, legs, into his head. He laughed, relieved, awestruck, as his veins bulged blue again and color-not much; he'd never been very tan to begin with-appeared in his skin.

"Clary, you did it!" Grateful beyond measure, Simon threw his arms around his stunned best friend, enveloping her in a tight hug.

She laughed, too, and it sounded like she was crying. "Simon," she said into his worn "Made in Brooklyn" t-shirt. "Simon, it's you."

"Yeah, Fray." He kissed her forehead. "It is."

She pulled away, grinning. "I think there's someone you should tell first."

"Church? Ah, yes, he has been awaiting this day for a long time."

"You know who I mean," Clary said, raising her eyebrows.

He did.

And he _did _want to tell her.

In the Institute.

In her bedroom.


	2. Chapter 2

**Chapter Two**

Simon stood in front of the Institute, never so unsure of anything in his life.

This was a big deal. The last time he'd entered this building, he'd been thrown half-dead onto the doorstep by the vampire who'd turned _him _into a vampire.

And he certainly hadn't come to the Institute to see Isabelle Lightwood.

It was nearly twelve in the morning. The war with Sebastian was coming, and the Shadowhunters were training harder than they had in their lives. Even if someone was energetic enough to answer the door, no one but Isabelle would let him in.

The thought of Maryse Lightwood, armed with a multitude of Shadowhunter weapons, swinging open the door to see her daughter's boyfriend at twelve A.M. no longer a vampire and fully able to venture into the Institute scared Simon enough to head around to the side of the building, where Isabelle's room was.

It wasn't _that _tall, he told himself as he managed to get a grip with his hands and feet on some outlying bricks in the wall. As he struggled to climb higher, though, he realized that perhaps the front door wasn't such a terrifying thing. But the thought of Isabelle, lying peacefully in bed, skin laced with runes and battle scars, looking like the vulnerable girl she really was inside, propelled him up, all the way to her window. He didn't look down.

The window was open, much to his relief. "Izzy?" Simon called quietly, pushing it open. "Isabelle?"

No response. He peered into the dark room, and saw that Isabelle's bed was empty. At twelve in the morning.

He hoisted himself up and crawled through the window, landing with mortal ungracefulness on the plush carpeted floor.

Where the hell was Isabelle? She couldn't be sleeping at Magnus's. Since he and Alec had reconciled a few days ago, they'd all been giving them space. Plenty of time alone to reconnect.

It only took Simon a few more seconds of thought to realize where she was. A war was coming. Isabelle was, well, Isabelle. He crept out of her room and down the hall to the training room and, sure enough, there she was. His girlfriend. Wearing his "I Blogged Your Mom" t-shirt.

"I was wondering where that shirt went," Simon said, and Isabelle jumped, turned to look at him, and dropped the knife she'd been preparing to throw at a target on the wall.


	3. Chapter 3

**Chapter Three**

Isabelle tried to blink sleep out of her eyes. She was exhausted; she'd been training since eight A.M. and only took a break to bring some Taki's to Magnus and Alec-and soon left, realizing they were a little too preoccupied to eat lunch.

But Sebastian was coming. He'd warned them. And she was determined to be the best Shadowhunter in the war. She was determined to kill Sebastian and his army. She was determined to avenge Max's death, to make him proud of her.

So she reached for another dagger on the wall beside her and slugglishly prepared to throw. Just as she was straightening her elbow, a voice broke through the eerie silence of the training room. A very familiar voice. One she knew she would never hear in this room, in this building, ever again.

__"I was wondering where that shirt went," Simon said, and the weapon fell to the ground, just missing her bare feet. First she felt her face flush with color; she didn't want him knowing that she often wore this shirt to sleep, that she wished she could spend the night with Simon more often, that she missed him like hell when she was stuck in the Institute all day.

Then she realized.

He was in the Institute.

"Simon?" She breathed, though it was obviously him.

In the dim witchlight illuminating the room, she could see him grin. "In the flesh," he said, "and blood."

She simultaneously wanted to run to him and throw her arms around him, feel his heart beating again, see the color in his face, wanted to see him wear the glasses she always secretly thought he looked adorable in, and stay right where she was. This wasn't real. There was no way to bring a Downworlder back; no way to make a vampire human. No way.

Isabelle sighed. She was just overtired. Dreaming, hallucinating, whatever wasn't reality. She would not let herself indulge in this fantasy only to wake up and be crushed with disappointment.

But Simon seemed very, very real when he closed the distance between them, cautiously at first then faster, with a small, slightly scared "Iz?" And when she felt him wrap his arms around her, squeezing her tightly, his heart beating rapidly against her back, she didn't care if she was dreaming or not anymore.

"Iz, it's me, I swear," Simon said softly, his words tickling her neck.

"I know." She smiled, and turned to face him. Even in the witchlight, she could see his human looks restored; his skin was no longer slate-smooth, no longer frighteningly pale. No longer inhuman. "How?" Isabelle asked, her voice barely a whisper, and she found herself reaching over to him and placing her hand on his chest, feeling his heart pound.

"Clary made a rune," he explained. "For . . . for my birthday."

Isabelle recoiled. "You didn't tell us it was your birthday."

"Well, technically yesterday was my birthday," Simon said.

"Simon!" She punched him, hard, in the shoulder.

"Ow."

"I would have gotten you a present, too."

"Izzy, it's really okay-"

She cut him off by, impulsively, leaning forward and pressing her lips to his. Softly at first, savoring the newly human feel of his mouth; it was softer, with the faintest hint of spearmint gum. She smiled as she kissed him, and she felt his hands on her face, tangled in her hair, felt his heart beating wildly through his t-shirt.

"Well," he said, breathing hard when she pulled away. "That was a great present. It might even top the Spiderman trading card set my sister got me ten years ago."

"You thought that was all?" Isabelle grinned, taking his hand. "You've obviously never celebrated your birthday with a Shadowhunter girlfriend before."

Simon was speechless as she led him carefully over the dagger she'd dropped, down the vast institute hallway and into her bedroom, closing and locking the door behind them.


	4. Chapter 4

**Chapter Four**

Isabelle had never been so happy in her life.

Not even the first day she'd gone demon-hunting with Alec and her father had given her the whip and her ruby pendant. Family heirlooms, he'd said. Now her whip was rolled up somewhere in a drawer in her room, and her pendant had swung around her neck and lay on her pillow, beside her ear, which Simon's lips were moving towards.

She giggled with pleasure, running her hands through his curling dark brown hair. His lips made their way back to her own, and she kissed him hard; he was lying practically on top of her now and she was glad she'd locked the door.

She was glad Simon was human.

She was glad Simon was hers.

She paused to sit back and slip out of his t-shirt she'd swiped weeks ago, when they were still staying at Magnus's. Simon hovered over her for a moment, staring at her lacy purple bra, and she grasped him by the collar of his shirt and yanked him back down, crushing her lips against his. He didn't object.

His skin was no longer frigidly cold, thanks to the blood flowing through it, but Isabelle still got chills when Simon peeled off his own shirt and tossed it aside; his stomach was harder than she'd remembered. She felt the beginnings of some ab muscles there.

"ISABELLE."

The shout was accompanied by the clattering of her door being flung open, despite the fact that she'd definitely locked it. Damn opening runes. Simon jumped with surprise, rolling agilely to her side and sliding under her mess of blankets.

"Try knocking next time," she sneered at her older brother who, admittedly, she was surprised to see standing in her doorway at twelve in the morning, disheveled but fully dressed in gear.

"What the _hell-" _Alec started, noticing Simon.

"He's human now. And what are you doing in here?" Isabelle demanded, anxious for him to leave.

Alec's expression was grave. "Sebastian is coming today."

"_What?"_

"He has an army," Alec explained. "It's much, much bigger than we thought. Full of demons we've never even heard of, never dared try to fight. We have to be ready."

"How do you know?" Isabelle's pulse raced.

"Fire message," Alec said, as if it should have been obvious. "Mom told me to warn you, if you were awake, which I guess you are." He shot a menacing glare at Simon.

"Relax, he's just a mundie," Isabelle said, annoyed at his protectiveness.

"Hey!" Simon protested.

"We're portaling to Idris at five A.M." Alec looked as if he hadn't slept in days. And, given that he'd been at Magnus's all week, he probably hadn't.

"Idris?" Isabelle's head spun. This was too much to process.

"Five A.M." Alec directed one more glare at Simon before turning and exiting the room. "Night, Iz. See you in the morning."

When he shut the door behind him, both Isabelle and Simon were frozen.

"This is Valentine all over again, isn't it?" Simon said quietly, breaking the silence after several moments.

"No." Isabelle shook her head. "This is worse. Sebastian wants revenge."

"How is that worse?"

"Because not only is his father the most hateful, ruthless Shadowhunter ever, but he has demon blood. At least Valentine _felt _things."

"Valentine is Clary's father, too," Simon pointed out.  
"Luke is Clary's father," Isabelle said firmly. "Valentine is dead. And by the Angel, Sebastian will be too."

"Iz . . ."

"He killed my baby brother," she said, and she was suddenly filled with so much rage and frustration at Sebastian's existence that she wanted to cry. She settled for leaning her head back against Simon's shoulder; he began stroking her hair, and the gesture comforted her slightly. Max used to stroke her hair when he was younger; he used to try to braid it. He thought it was hilarious.

"And he's going to pay for that," Simon assured her. "He's going to get what he deserves."

"That's not all," she said, her voice strangled. "Simon, now that you're mortal . . . you can't come to Idris with us."

Simon froze.

"This could be the last time we see each other." Her voice was barely a whisper. "This could be goodbye, Simon."

"No."

"There are laws-"

"None that any of you follow."

"It's different in Idris-"

"There has to be a way." Simon sat up, so Isabelle did, too. He took her face in his hands and stared into her eyes intently. "I love you, Isabelle Sophia Lightwood, and I'm not going to leave you for anything."

Isabelle felt a grin melt over her face. "Simon . . ." An idea was forming in her mind, but she wasn't sure she could say it. She wasn't sure if it was even possible. All she was sure of was that she loved Simon, too, with all her heart; with every last piece of her broken heart. Because she knew he wouldn't break it any further.

"Yes?"

She had to say it. She had to be with Simon. She couldn't die in Idris knowing he would live the rest of his life here, in New York, dating and marrying ordinary mundane girls. She couldn't.

"There might be a way," she said hesitantly.

"Which is?" He was hopeful.

She took a deep breath.

"You could Ascend. You can become a Shadowhunter."


	5. Chapter 5

**Chapter Five**

"Isabelle," Simon said seriously, realizing he hadn't called her by her full name in a long time. "This isn't like buying a pair of shoes. You can't just decide to become a Shadowhunter that quickly."

Isabelle frowned. "Do you know how long it takes me to decide on a pair of shoes?"

"This is permanent," Simon continued, voicing his own thoughts. He'd just begun to enjoy being human again. He couldn't even imagine being a Shadowhunter. "There's no going back."

"Why would you want to?"

Simon knew he had to phrase this carefully. He thought Shadowhunters-Isabelle, specifically-were amazing and didn't want her thinking he felt otherwise. They were strong and brave and independent and warriors. But he wasn't any of those things. He was just Simon. He was a mundane. "There isn't even time," he tried. "Not before five o'clock."

Izzy looked like she was trying hard to mask disappointment. "You don't want to be with me," she said, voice wavering slightly.

"No, no!" Simon said quickly. "All I want is you." And he meant it.

The idea turned in his mind. If being a Shadowhunter was what it took to be with Isabelle, then he would be one. He would endure the training and learn to fight and go to war with Sebastian. He would protect her. Not that Isabelle needed protecting; Clary, on the other hand . . .

"Consul Penhallow is here, in the Institute," Isabelle said, her face lighting up with excitement. "She can perform the ceremony. We're desperate for fighters, Simon, and she knows that you helped us in Idris the last time."

Simon considered this. Shadowhunters were exclusive. They did not want ordinary mundanes becoming part of their race, and certainly not someone who was so recently a Downworlder. But Isabelle had a point; these were desperate times, and he'd learned some techniques from watching Clary, Isabelle, and Alec fight over the past year.

"Besides," Isabelle said, her voice lower. "I can't marry a mundane."

Simon nearly choked.

"I'm _kidding," _she insisted, smacking his shoulder again. Her smile was reassuring. "Come on, let's go get the Consul."

"Now?" Simon asked incredulously.

"Well, I might put on some clothes first."

He moved to let her off the bed, and watched as she dressed swiftly in gear, strapping a weapons belt around her waist. He watched her scars, the faint silvery traces of past runes she'd drawn, the new and darker ones. She was so beautiful, he thought. And even though he knew she was just joking, in that moment he didn't find it too crazy to imagine spending his life with Isabelle Lightwood.

"You coming?" She gestured toward the door, practically bouncing on the tips of her feet.

"I think I might get dressed, too," Simon said, gesturing to his bare chest.

"I'll be in the hall," she said. "I'm going to tell Alec."

After she left, Simon sat for a moment, letting this sink in. He was going to become a Shadowhunter.

Without really even thinking about it, he slipped his cell phone from his pocket and, as he redressed, he dialed Clary's number.


	6. Chapter 6

**Chapter Six**

"Fray?"

"Why do you sound so nervous? And why are you calling _me _when you should probably be talking to Izzy-"

"I have to talk to you about something important," Simon said, and in the background, he heard an all too familiar voice sigh. "Can't it wait?" Jace said impatiently.

"Shhh!" Clary snapped.

"Tell Simon he's got the worst timing of any vampire or mundane I know."

"I'm not going to tell him that!"

"Nice to talk to you, Jace," Simon said, a little annoyed and wondering if he'd been hiding in Clary's closet all night, waiting for him to leave. "But I really would like to talk to Clary more."

"I'm alone now," Clary told him a few moments later. He heard a door shut. "What's going on? Is everything okay?"

"Izzy wants me to become a Shadowhunter," he blurted.

"Is that even possible?"

"Thanks for the support, Clary. Love you, too."

"I just _meant _that isn't it more of a process? And it's not like you've trained or anything."

"Sebastian is coming tomorrow," Simon said, figuring someone would eventually break the news to her and why shouldn't it be him? "He's coming to Idris and all the Shadowhunters are going to fight him. They need people. I can help."

"But you're doing this for Isabelle."

"Maybe."

"_Simon."_

"Yes?"

"You're going to give up your whole life, your whole human life, for love?"

"Don't act like you haven't done the exact same thing. And when you did it, you were under the impression that your love was your brother. So, really, this doesn't seem so bad."

"I was born a Shadowhunter," Clary reminded him. "I was meant to be a Shadowhunter. You're not."

"Again, thank you for the overwhelming show of support."

Clary sighed. "Simon, I'm just worried about you. I don't want you to die."

This angered Simon. "Do you think I'm not worried about _you _every time you go off to battle with demons? Do you think I'm not scared for your life every single day?"

"I had to do this," Clary said. "You don't."

"I know."

"But you're going to, aren't you?"

"Yes."

Despite her trepidation, Simon could practically feel his best friend smile over the phone. "Then I will be thrilled to fight beside you, Simon Lewis."

"SIMON!" The voice was Isabelle's; it was anxious. "Come ON!"

"I have to go," Simon told Clary. "Thanks, Fray."

"Anytime, Lewis."

Simon hung up the phone, hoping she'd meant what she'd said.

_I will be thrilled to fight beside you._

"By the Angel, what took you so long?" Isabelle, impatient as ever, stormed into the room, grabbed hold of his wrist, and yanked him out through the doorway, towards the Consul's room.


	7. Chapter 7

**Chapter Seven**

"Isabelle Sophia!" Maryse Lightwood scolded when Isabelle dragged Simon into the Consul's room. It was larger than the others, at the end of the hall; she and Consul Penhallow were seated at the small square table in the middle of the room, looking exhausted.

"This is important," Isabelle insisted, not feeling the slightest bit guilty for barging in on their meeting.

"Did Alexander not tell you of our plans tomorrow?" Maryse was frustrated.

"That's why I'm here." Isabelle turned to Jia. "Hello, Consul Penhallow."

"Lovely to see you, Isabelle." She smiled kindly. "Can I help you-" She stopped when she saw Simon. Judging by her mother's shocked expression, Isabelle guessed she, too, had realized her formerly vampire boyfriend's presence.

"OneofClary'srunesturnedSimonbackmortal," Isabelle explained in a rush. "Anyway, we're going to war tomorrow. Correct?"

Jia hesitated. "_War _is a very strong word, Miss Lightwood . . ."

"But that's what we're doing."

"_Isabelle-"_

She ignored her mother's imploring gaze. "Consul, I have a very, very big favor to ask of you."

"Yes?" She looked a bit nervous.

"Simon would like to become a Shadowhunter," Isabelle said, and saw Maryse already starting to object. "We need fighters tomorrow, and Simon may not be properly trained, but he once fought off a Greater Demon from Alec, Clary, Jace and I. He fought in the Mortal War against Valentine and survived. He's strong, Consul, and he's ready."

Maryse looked as if she wished she'd never had children. "Isabelle," she said quietly, "I understand that you may have feelings for Simon. But that is no excuse to treat the process of Ascension as something so frivolous."

"It's all right," Simon said firmly. "I just wanted to help. I don't want to cause any stress here."

"Simon," Consul Penhallow said seriously, "Do you truly believe you are prepared to become a Shadowhunter?"

"Yes," Simon said, with no hesitation. "Yes, I'm ready."

Isabelle squeezed his hand.

"I admire your devotion," Jia said, smiling at him. "But I cannot perform the ceremony if you are doing this for the sole purpose of remaining connected to Miss Lightwood."

"No," Simon said, releasing Isabelle's hand. She peered at him curiously, and found that he indeed appeared more confident than she had ever seen him before. "No, Consul. As you probably know, I was recently a vampire. And while I was a vampire, I never quite accepted it. Not just the immortality, but what their species stands for. And I observed my friends, your Shadowhunters, while I was a Downworlder and even when I was still human, in awe every day of how brave and strong-willed they were. You all stand for something; you stand for the protection of mundanes and your own species, and you don't stand for murder or violence or war, even though those things always seem to find you. Being human isn't enough. Not anymore. Humans aren't as good as you, they never will be. Not just because of your strength and your fighting and your weapons, but your beliefs. You strive for peace, for the eradication of evil. And more than anything, I want to be a part of that."

Maryse and Jia were both silent for several stunned moments. They were clearly impressed, and so was Isabelle. For once, she had no words for Simon; she wanted to thank him for some reason, and she wanted to kiss him, and she wanted to train him to fight. She settled for taking hold of his hand again and gripping it tightly. She did not intend to let go for a long, long time.

"You truly do seem to know what you want, Simon Lewis," Jia said. "And you seem to understand our race perhaps better than we understand ourselves."

"No-"

"I mean that in a good way." She smiled. "Simon, if you are still willing, I will appease Isabelle's demand of making you a Shadowhunter."


	8. Chapter 8

**Chapter Eight**

"How does it feel?"

"Izzy, you know what it feels like to be a Shadowhunter."

"Not a _new _Shadowhunter," she said, running her fingers lightly along the new runes snaking up and down his arms. They'd burned more than he'd expected them to, and it still felt odd to see them on his own skin, but he meant it when he said, "I feel stronger."

Izzy grinned. "You _look _stronger."

Simon raised an eyebrow. "Strong enough to fight Sebastian?"

"Strong enough to fight an army of Sebastians."

"We could have to," Simon said. "For all we know, he's cloned himself."

Isabelle giggled. "Probably."

"So, Izzy," Simon said seriously, moving a bit farther away. They were both sitting on the bed in what would be his room in the Institute, should he survive the war. "Even if I can come with you to Idris and fight now, this could still be goodbye."

"No," Isabelle said firmly. "I won't let it be. You're not leaving me, Simon. And I won't leave you."

"But if-"

"No ifs." She brought her finger to his lips, quieting him. "We're not going to die. Fighting doesn't mean dying, you know."

"Yes, but-" Simon spoke around her finger.

To stop him this time, Isabelle used her lips. She leaned over and kissed him, hard, surprising Simon. He kissed her back, running his fingers through her thick wavy hair, trying to memorize the feel of her mouth on his. The curve of her cheekbones. The excited spark in her eyes when someone mentioned demons, a battle.

For the second time that night, they were interrupted.

"Guys." It was Clary. "Sebastian is here."


	9. Chapter 9

**Chapter Nine**

"By the Angel, Simon," Clary gasped; Simon and Isabelle were both too stunned to say anything. "You really did it."

"When you say _here-"_

"He's in New York," Clary rushed to explain, still marveling at Simon. "He's coming for the Institute. And he's got an army of demons _and _Dark Shadowhunters with him."

"This is bad." Isabelle leaped up from the bed, began pacing the room. "We're not prepared . . ." She thought of all the Shadowhunters who were ready to fight, in Idris, hundreds of fully trained Shadowhunters and Downworlders determined to defeat Sebastian. Here, they only had the Lightwoods, Clary, a handful of Clave members, Jocelyn, Luke, and Simon. Maia and Jordan had portaled to Idris to discuss Downworlder terms with the Clave there days ago.

"I don't have a rune for unexpected, brutal attack," Clary muttered.

"How do you know he's in New York?" Simon asked.

"We have lookouts everywhere." Clary appeared to be out of breath. She was panicked.

"They're not very _good _lookouts."

The voice that came from behind Clary chilled Isabelle to the bone. It was not Jace who casually sauntered up beside Clary in the doorway, but Sebastian himself.

Clary, wide-eyed, whirled around to see her brother, towering over her. Fully dressed in gear, white-blonde hair shading his cold black eyes. A sadistic grin twisted his face, and Isabelle instinctively reached for her weapons belt; unfurling her whip in the process. She felt a small spark of pride when she noticed his lack of a left hand.

_I'm going to kill him for you, Max, _Isabelle thought firmly. _He's going to pay. _

"Whoa, there," Sebastian said, still smirking; he raised his arms as if to defend himself. "I did not come to fight. At least, not immediately."

"Then what _did _you come for?" Clary's voice was full of acid; laced with bitterness. Hatred. Isabelle couldn't imagine feeling that strongly against her own brother; she felt lucky to have Alec.

"Ah, the Daylighter's a Shadowhunter," Sebastian observed, slowly moving towards Simon. Isabelle moved to block him, to protect him, and Sebastian laughed at the gesture. "How did that come about, little sister?" He raised a suspicious eyebrow at Clary.

"Remember," Clary said through her teeth, looking more powerful than Isabelle had ever seen her as she moved towards Sebastian. She stopped just a few feet short, right in the middle of the room. "I may not have an army. But I have this." She withdrew her stele from her weapons belt, brandishing it in front of her. "And I am much more powerful than you."  
Again, Sebastian cackled wickedly. "Oh, little sister. You do make me laugh." Then, shocking Isabelle, he threw his arm out in front of him, hitting Clary and knocking her to the ground.

"Clary!" Simon shouted, leaping off of the bed and trying to run to her, but Sebastian hit him, too; he flung him to the other side of the room, all the way to the wall.

"You psycho bastard," Isabelle snarled, readying her whip. "You _demon." _She snapped it, and heard the electrum whistle through the air towards Sebastian. But he was just as fast.

Somehow he curled it around his wrist, yanking it; Isabelle refused to let go of her whip, her only real defense. She fought him, boots skidding along the wooden floor of the bedroom, but he still managed to pull her close to him. Then he flung her back, and after a terrifying moment of being airborne she collided with a bedpost, felt something in her back crack, and sunk to the ground. She thought she heard Simon shout her name, too, but she didn't care. She was fuming, not just at the injury but _him. _How _dare _he break into her house and attack everyone? How _dare _he even lay a finger on her little brother?

"You won't beat us," Clary hissed, rising unsteadily to her feet.

"I already have," Sebastian smirked. "Look." He gestured to the window. Simon and Isabelle rose with Clary, and they all walked shakily, nervously, to the window. In the dim light from the just-rising sun below, on the lawn, they could see a portal. Through it, people were pouring through. Not just people. Shadowhunters. Dark Shadowhunters. They moved languidly, following each other blindly, soldierlike, towards the front doors of the Institute.

Isabelle gasped when she recognized one. Just one. But she knew him so well. He was the one who'd given her her whip, her ruby necklace that alerted her of demons' presence, who taught her how to fight.

He was her father.


	10. Chapter 10

**Chapter Ten**

Isabelle was consumed by a new kind of rage, a new hatred for Sebastian. But she didn't have time to act on it, because Clary did first.

Her _parabatai _(they'd performed the ceremony two weeks ago) lunged for her brother, taking him by surprise this time. She'd gotten hold of a seraph blade and shouted _Raziel _as she neared Sebastian, and she stabbed the blade right through his shoulder.

Sebastian didn't even flinch. He just rolled his eyes, annoyed as he calmly removed the blade and glared down a stunned Clary, who was backing away.

Isabelle knew this was her chance to get him. She drew her whip back towards her, coiling it around her wrist, and released it on Sebastian, flinging it towards his arm. She'd been aiming for his head, honestly, but the pain in her back was throwing her off.

This time, it got him. The electrum wrapped around the wrist of the hand that he still had and his eyes widened before Isabelle gave the whip a pull, and off came his other hand.

Black, viscous demon blood cascaded out of the wound, spattering the floor of what would be Simon's room, if he survived this. "_Isabelle!" _Simon shouted, almost in protest. Isabelle knew her mother would panic if she saw the mess, and she wondered briefly, terrified, if Maryse was still alive. If her father had any chance of being alive again.

"Bitch," he hissed, grasping for his wrist; just as he had in Idris. But now he had no hands to grasp it with; he had no way to fight.

She thought.

Moments later, his hand began to grow back. It was much, much paler than the rest of his skin and free of any runes, but it was still a hand. Regenerating.

"What the hell?" Izzy cried.

"Did you really think," Sebastian snarled, furious now, "That you could defeat me, you deranged little bitch?"

"Actually," Isabelle said, "I do."

"You're wrong."

"_You're _wrong."

The voice came from the doorway. It was Jace, who stood beside Alec. "If you ever threaten my sister again," he growled, "I'll kill you. Well, I'll kill you regardless, but it'll be more painful."

"Well," Sebastian said, amused. "The whole of Team Good is here, aren't they? Brimming with false confidence and a few seraph blades. Pathetic."

An arrow zipped right by Sebastian's face. It was Alec's.

"Next time it'll be in your eye," Alec snapped, "If you don't leave right now."

"You don't frighten me," Sebastian stated, glaring at Alec. "I know you're willing to throw your life away to fight me. The broken-hearted always are."

So he didn't know that he'd gotten back together with Magnus. _He _hadn't discovered they were together by bringing coffee to Magnus's apartment as a friendly gesture and found them-

Isabelle shuddered.

Alec brandished a seraph blade and so did Jace, and they both lunged for Sebastian. Sebastian slipped his own blade from his pocket. It was darker, gray, not clear, and unlike anything Isabelle had seen before.

"Perks of being part-demon," he smirked. "Better seraph blades."

He swung it towards Alec, who ducked the first time and rose again to hit Sebastian, but Sebastian stuck him with the new blade. Right through the shoulder.

Alec gasped, grasping for his shoulder, and sunk to the ground. Isabelle dove to help him, horrified. _Don't die, _she thought. _Don't leave me._

"Only warlock magic can heal him now," Sebastian cackled. "And now that you're out of touch with, who was it, Magnus? He's got no chance."

"Take him away," Isabelle begged Jace, who stood frozen, watching his _parabatai _fall in horror. "_Take him," _she ordered. _To Magnus, _she implied.

Jace looked at Clary.

"I'm fine," she insisted. "Go."

"We're not done yet," Jace growled at Sebastian, who was still smirking. Isabelle would kill him, she would. Jace helped Alec to his feet and out of the room, down the hall, out of sight.

Before Isabelle could turn back to face Sebastian, she heard him let out an eardrum-rattling shout. There was a huge gash on the side of his face, and Simon was wielding a bloody dagger.

"_Simon?" _Isabelle just had time to gasp before Sebastian howled with rage and dove for her boyfriend, who looked just as surprised as she was. She and Clary both shouted out in protest at the same time, to no avail. Sebastian hit Simon with the same blade he'd stuck Alec with, but he got Simon square in the chest.

He'd stuck it through his heart.

Simon was no longer immortal.

"Stupid girl," Sebastian snarled at Izzy. "These don't effect vampires."


	11. Chapter 11

**Chapter Eleven**

Isabelle knew she was supposed to fight. She knew she was supposed to follow Clary as she chased Sebastian out of the room, moving as lithely as if she'd been training her whole life. She knew she probably should have taken Alec to Magnus rather than Jace. She knew she was not fulfilling her duty as a Shadowhunter.

But she could not leave Simon.

"It hurts, Izzy," Simon said, through his teeth, gripping the blade still embedded in his chest, through his t-shirt.

"Simon." Isabelle felt tears swell behind her eyes, threatening to spill over. She knelt beside him, shedding her whip and seraph blades and wanting to shed everything in that moment; being a Shadowhunter. If they were just _people_, mundanes, they wouldn't have to deal with this. Simon's life wouldn't be compromised on a regular basis.

"Simon, I need to see it," Isabelle said softly, listening to him breathing hard. _Don't stop breathing._

"Not the way I expected you to see my shirtless today, but all right." He cracked a smile.

Isabelle moved the fabric aside, unsure whether or not to remove the blade. She nearly recoiled when she saw the skin underneath, surrounding it; black fissures were spreading from the wound, all across Simon's chest, rapidly.

"Take it out," Simon said, his voice calm. "Please, Iz. I'm fairly certain it's killing me."

Isabelle hesitated. "This is going to hurt."

"Let it."

She wrapped her fingers around the blade and immediately withdrew her grip; she felt like she'd just grabbed a hot curling iron.

"Please." Simon was obviously struggling to keep his voice even.

Isabelle gritted her teeth and drew her sleeve over her hand, using it to grab hold of the demonic blade and pull. She got it out and promptly dropped it onto the floor; it rolled towards the door.

Simon let out a small sound of agony, reaching for her hand. Isabelle gripped it tightly, so tightly she knew she must be hurting him, but he only held her tighter as well. Bracing herself, Isabelle peered at Simon's bare chest; black, viscous liquid was seeping from the wound, mixed with red. Mixed with his blood.

"I'm so sorry, Simon," she said, and she let herself cry now. Sobs racked her body. This was her fault. Everything was her fault. Her younger brother was dead, her older one severely injured. Her _parabatai _was fighting the most evil Shadowhunter of their kind with no assistance. Her father was Dark, her mother might be dead. Simon was all she had. And he was leaving her.

"It's not your fault, Iz," Simon assured her, trying to sit up, but it clearly pained him too much.

She wanted to wrap her arms around him, feel his newfound heartbeat, his strong Shadowhunter blood. She wished _she _was the one dying, the one suffering in his place.

"It is." Isabelle ran her hands through his hair, watching his eyes struggle to stay open, to stay alive. "And I don't know how to fix this."

"I can help you."

The voice came from the doorway, shocking her. Isabelle whirled around, moving protectively to shield Simon. But it was just a woman. A woman in modern-looking gear and a stylish scarf. She had piercing gray eyes and brown hair pulled back into a braid. But she was holding a book. The Gray Book. And a stele.

"Who are you?" Isabelle asked, her voice barely a whisper.

The woman-who didn't look much older than she was-smiled. "My name is Theresa Herondale," she said, "But you can call me Tessa."


	12. Chapter 12

**Chapter Twelve**

"How did you get the Gray Book?" Isabelle asked, as Tessa strode into the room. _And how is your last name Herondale?_

Tessa smiled. "I wrote it, Miss Lightwood."

_How do you know my name?_

Dozens of questions welled up in Isabelle's throat, but she didn't want to ask any of them now. She did not want to waste any time that could be spent healing Simon.

Tessa approached them and knelt on the other side of Simon.

"Nice to meet you," Simon managed, and the mysterious woman smiled. She opened the book on her lap and flipped to a page near the end.

"Do you know anything about demonic seraph blades?" Isabelle asked her.

Tessa nodded, appraising Simon's chest. The fissures were deepening, spreading faster. "Someone could create them, only with the help of a Greater Demon."

Lilith.

"Why have I never heard about them?" Isabelle knew it was slightly selfish, but she took pride in knowing as much as she possibly could about everything Shadowhunter-related; weapons included.

"They don't teach you things like that, because they don't want you making things like that," Tessa said. "But Jonathan Morgenstern wasn't exactly educated by the Clave."

"Can you save him?" Isabelle asked, pleading in her voice.

"I will do my best," Tessa promised, settling on a page in the Book. She scanned its words, and drew her stele. She settled it directly above Sebastian's wound, and Isabelle gripped his hand so tightly she was certain she was cutting off his circulation.

Isabelle watched as Tessa began to draw, runes she'd never seen; they weren't too different from the ones she knew, but still different. She drew six, all in a circle around where Sebastian had stabbed him. Almost in the heart. But not quite; Simon was still alive.

Simon gasped suddenly, grabbing at his throat, like he couldn't breathe.

"Normal side effect," Tessa assured Isabelle. Simon soon began breathing again.

"Are they working?" Isabelle asked, panicked. "Is he okay?"

"Look," Tessa said, and Isabelle did.

The runes were fading, but so were the fissures that had cracked Simon's skin just moments ago. His skin was retaining its pale but clearly alive pallor; he was going to be all right. He was going to survive.

Isabelle could have cried out with relief.

"You'll need to monitor him," Tessa said sternly, still watching his chest. "No fighting for him, not yet. He will heal, but only with time and rest. There may be traces of demon ichor still in his skin, which could slow him down."

Isabelle never hugged anyone, but she could have hugged Tessa then. "Thank you, thank you so much." She grinned down at Simon. "How do you feel?"

Simon managed to sit up slightly. "Better than Sebastian's going to after you get your hands on him."

Isabelle smiled. Then she glanced up at Tessa, who was leaving the room.

"Thank you," Simon called gratefully after her. She only paused; she did not look back.

"You said your name was Herondale," Isabelle pointed out, her curiosity getting the best of her. "How is that possible? Jace is the last Herondale left."

"Not quite," Tessa said cryptically, still not turning around.

"Tessa, are you all right?" A boy about her age, with spiky black hair and dark eyes, appeared in the doorway. He was fully dressed in gear.

"I'm fine, Jem," said Tessa. "So is the new Shadowhunter." She tipped her head slightly back towards Simon.

The boy-Jem-glanced up and noticed Isabelle. A smile quirked his lips. "You don't look like a Lightwood," was all he said before he took Tessa's wrist and pulled her down the hallway, away from Simon's room.

Isabelle sat, stunned, for a moment. What did he mean, she _didn't look like a Lightwood? _She looked exactly like a Lightwood. She _was _a Lightwood.

"Iz?" Simon said, pushing himself to his feet. "Isabelle, we have to go fight."

"You heard what Tessa said," Isabelle told him, lightly pushing him back. "You have to rest."

"Isabelle," he said, "There's a war going on. I'm going to fight. It's why I became a Shadowhunter in the first place."

Isabelle grinned. "I forgot about that."

And with newfound respect, she let him take her hand and lead her down the hall to fight, just as Jem had led Tessa.


	13. Epilogue

**I'm not going to write any more battle scenes because I suck at them and I don't want to write COHF because that's Cassie's job. But I do want closure for this story and I love Sizzy so here you go :)**

* * *

**Epilogue**

"I have a birthday present for you."

Tess, who had just turned five that day, glanced up at Isabelle as she strode into her daughter's room. She was curled up beside Simon on the bed, reading one of his old comic books.

"You already got me a present," Tess said, brushing some dark curls out of her big brown eyes.

"This isn't a normal present," Isabelle told her, sitting across from her on the bed. "This is a Shadowhunter present."

Tess's eyes widened. She knew little of the Shadow world; they'd told her stories (abridged versions), she'd seen her cousins Seraphina and Will (Jace and Clary's children) train. But she knew that it was exciting. More exciting than the mundane life she wouldn't have.

"Here," Isabelle said, and drew her ruby pendant from behind her back.

"Iz . . ." Simon's eyes widened, too, at the object. He hadn't known she would be willing to give it away.

"Ooh," said Tess, reaching for it. She held it, examining it, her eyebrows furrowed together. "Pretty," she decided.

"It will keep you safe," Isabelle promised. "It will glow when demons are close. Do you remember what demons are?"

Tess nodded.

"But you don't have to wear it yet," Isabelle said, much to Simon's relief. "You won't start training-"

"Until I'm eight," Tess finished, frowning. Isabelle knew she wanted to train now, to catch up with her slightly older cousins, but she wasn't ready. And Izzy wasn't quite ready to let go of her just yet.

"Happy birthday, Tessa Clarissa Lightwood," Simon said, kissing her forehead and sliding off of the bed. Isabelle did the same.

"Night," their daughter said, and as Izzy shut her bedroom door, she could still see her turning over the pendant curiously in her hands.

"It's a family heirloom," Isabelle explained as she and Simon made their way down the hall of their apartment to their own bedroom. "It was my great-great grandmother Cecily's."

"Tess reminds me of you," Simon said. "She made Seraphina teach her demon-fighting techniques at the party today."

Isabelle smiled. They'd named her after Tessa, the mysterious woman-whom they suspected was a warlock-who had saved Simon's life. And Simon had taken the last name Lightwood when he became a Shadowhunter.

"I'm glad we made it out of the Mortal War alive," Simon said, and after Isabelle had slipped into bed, she watched him trade his jeans for sweatpants, and before he could put on his shirt, she grabbed hold of his wrist and spun him around to face her. He brought his lips down to hers, and she kissed him hard.

"I'm glad we're alive, too," Isabelle said, running her hands up and down his now-muscly arms, which were spiraled with runes. And she meant it. She was so, so grateful as Simon climbed onto the bed with her, hovering just above her as they kissed. He was hers, and he would be hers forever.


End file.
